Hi, I've just bought a 2001 A6 and am experiencing some trouble with the auto gearbox. From cold, everything is fine, but after the car has been going for 1/2 hour or so the gear changes become very ragged between 1500 & 2500 rpm. Could something be overheating? I don't think its engine management trouble because its not a constant problem. The manual Tiptronic element works fine.

Thanks.